1. Field of the Invention
The present invention relates to a pointer type indicator for indicating a measured value with use of a pointer, and more particularly, to a structure improved in assembling electric elements.
2. Description of the Prior Art
Heretofore, this kind of pointer type indicator has been used as a fuel gauge for indicating an amount of remaining fuel, a water temperature gauge for indicating a temperature of water coolant, or a voltmeter for indicating a voltage of a battery, in a vehicle such as a motor vehicle or the like.
Also, a meter device in which a plurality of different measured values as mentioned above are respectively indicted by employing a plurality of indicating mechanism is called a combination meter, and has been widely used.
For example, Japanese Patent Application Laid Open No. 5-319140 (which will be referred to as a "first conventional device") discloses an example of such a combination meter.
The first conventional device comprises a dial plate with transparent index portion formed in the front surface thereof, according to items to be indicated, such as an amount of remaining fuel, speed of a vehicle, RPM of an engine, temperature of a water coolant and the like, pointers provided for respective measured values, an optical guide plate made of transparent resin material, a circuit board with a wiring pattern for signal transmission, and the internal mechanism for driving the indicator pointers.
The optical guide plate is provided on the back side of the dial plate, and the circuit board is provided in the back side of the optical guide plate.
Through holes are formed in the dial plate, the optical guide plate, and the circuit board, such that the holes penetrates these plates and board. Drive shafts extending from the back side are exposed through the holes. The drive shafts are mounted on the respective internal mechanism, and are driven and rotated in accordance with electric signals corresponding to the measured values.
The pointers are mounted to the drive shafts from the front side of the dial plate. Thus, the pointers are driven to respective angles corresponding to the measured values in accordance with electric signals supplied to the internal respective mechanism.
On the contrary, the internal respective mechanism for driving the pointers is positioned at the back side of the circuit board, and is fixed to the optical guide plate through the circuit board. Through this fixture, the electric connection between the internal respective mechanism and the circuit board can be performed.
Illuminating light from a light source is introduced into the optical guide plate, and the indexes formed in the dial plate and the pointers are illuminated by the illuminating light.
The light source for providing the illuminating light to the optical guide plate is formed into a module, and is fixed to the optical guide plate through the circuit board, like the internal mechanism as explained above. This fixture serves to form electric connection between the illumination module and the circuit board.
Since the conventional device as described above is constructed such that the internal respective mechanism and the illuminating light source or light source module are directly connected to the optical guide plate, advantages are obtained in that the number of components is reduced and that thus provided device has a small size.
However, in the first conventional device, since a member for diffusing the illuminating light is constituted only by the optical guide plate which is relatively thin, there is a problem that it is difficult to illuminate clearly and uniformly the entire dial plate because of loss of light introduced into the optical guide plate.
The problem of the first conventional device as described above can be solved, for example, by a technique of a device (which will be hereinafter referred to as a "second conventional device") disclosed in a micro-film of Japanese Utility Model Application Laid Open No. 51-11356.
Specifically, the second conventional device is provided with a first reflecting layer which is in contact with the optical guide plate and covers the back surface thereof, and a second reflecting layer from which figures of characters are removed. In this manner, illuminating light introduced into the optical guide plate is repeatedly reflected by the first and second reflecting layers so that illuminating light extends over the entire area of the optical guide plate.
In the optical guide plate of the first conventional device as described above, rugged portions are formed on the periphery or the surface of the optical guide plate in order to ensure the strength of the plate itself as a component, to make connection with another component, or to guide the illuminating light to pointers if the display device is equipped with illuminated pointers.
Accordingly, if the teaching of the second conventional device is intended to aggregate with the first conventional device, it is necessary to take such rugged portions into consideration.
In this case, it is difficult to adopt a normal thermal transfer method for forming reflecting layers as described above, and therefore, the reflecting layers must be formed by any different method such as a spray coating method for applying reflective material or the like.
If such a different type of applying method is employed, the manufacturing process becomes complicated, and resulting in problems of lowering the yield rate and increasing the manufacturing cost for manufacturing a required device.